What Is HDMI CEC?

HDMI CEC, short for Consumer Electronics Control, is a low-speed control bus that runs alongside the video and audio in every HDMI connection. It was defined in the first HDMI specification, published in 2002, and extended in later versions. The CEC wire must be present in every HDMI cable and port, but supporting CEC in a product is optional, which is why it works well on some equipment and not at all on others.

CEC uses pin 13 of the standard HDMI connector. It is a single-wire, bidirectional bus based on AV.link, the control line used on SCART connectors, and it runs at only around 400 bits per second. That is plenty for short commands such as “power on” or “volume up”. Each device on the bus takes a logical address, so up to 15 devices can share one HDMI chain, and each gets a physical address from where it is plugged in.

Because the CEC line is separate from the high-speed video signals, a TV in standby can still hear a CEC command and wake up. This is what lets a media player or console switch on the screen as soon as it starts.

The HDMI specification defines a set of CEC features. Manufacturers choose which ones to support, so two CEC devices may share only some of them.

Few TV menus say “CEC”. Most manufacturers use their own trade name, so the setting is easy to miss. Samsung calls it Anynet+, LG uses SimpLink, Sony uses Bravia Sync, Panasonic uses VIERA Link and Philips uses EasyLink. Some TVs, projectors and streaming devices simply list it as HDMI-CEC or HDMI device control. The underlying protocol is the same, so different brands usually work together for basic power and input control, but extra features often only work between devices from one manufacturer.

Most PC graphics cards and integrated GPUs do not drive the CEC pin at all, so plugging an ordinary computer into a TV gives no CEC control. Native CEC is far more common on Arm system-on-chips used in set-top boxes, Android media players and boards such as the Raspberry Pi, which is one reason a Raspberry Pi signage player can switch a TV on and off.

There are two common ways to add CEC to an x86 computer. A USB-CEC adapter sits in line with the HDMI cable and exposes the CEC wire over USB. Alternatively, DisplayPort 1.3 and later let a DisplayPort-to-HDMI adapter tunnel CEC over the DisplayPort auxiliary channel, although only some adapters support it. On Linux, the kernel CEC framework and the libcec library let software send CEC commands either way.

For signage, the screen’s control interface matters as much as the player. Professional displays usually offer RS-232 or network control alongside CEC, and displays with an OPS slot let a plug-in OPS computer control the screen through the slot itself.

Many of our digital signage players have a COM port alongside their video outputs, which is the usual way to schedule and monitor professional screens over RS-232.

CEC’s flexibility can also make it unpredictable. Each manufacturer implements a different subset of commands, so a soundbar may wake the TV when it should not, two sources may fight over which input is active, and some HDMI switches, splitters and extenders block or mangle CEC messages. Most HDBaseT extenders are designed to carry CEC with the video, but check before relying on it over a long run. If a TV keeps switching inputs or turning itself on, check the CEC setting on every connected device and turn it off on those that do not need it. On signage screens that should only be controlled by the player, it is often best to disable CEC entirely and use RS-232 or network control instead.

We supply signage players and OPS computers with the display control your screens support, whether HDMI CEC, RS-232 or network control, and configure it as part of each build as standard.